How is it possible and how is the transmission of information over wireless networks (mobile networks, wi-fi, bluetooth, etc.), if it is possible to explain? Information transmission When data transmission through communication channels began.
3.1 Types of communication and modes of operation of messaging networks
The initial types of messages can be voice, images, text, data. To transmit sound, the telephone is traditionally used, images - television, text - the telegraph (teletype), data - computer networks. Transmission of documents (text) can be coded or facsimile. To transmit sound, images and data in a single environment, networks called integrated service networks are used.
The code transmission of messages between drives located in the nodes of the information network is called teletext (as opposed to telex - teletype communication), and facsimile communication is called telefax. Types of teletex: e-mail (E-mail) - messaging between two network users, file exchange, "bulletin board" and teleconferences - broadcast messages.
Establishing a connection between the sender and the recipient with the ability to exchange messages without noticeable time delays characterizes the mode of operation on-line ("on the line"). With significant delays in storing information in intermediate nodes, we have an off-line mode ("out of line").
Communication can be one-way (simplex), with alternate transmission of information in both directions (half-duplex) or simultaneous in both directions (duplex).
3.2 Protocols
Protocols are a set of semantic and syntactic rules that determine the behavior of network functional blocks during data transmission. In other words, a protocol is a set of agreements regarding the way data is presented, ensuring their transfer in the right directions and the correct interpretation of data by all participants in the information exchange process.
Since information exchange is a multifunctional process, the protocols are divided into levels. Each level has a group of related functions. For the correct interaction of nodes of different computer networks, their architecture must be open. These goals are served by unification and standardization in the field of telecommunications and computer networks.
The unification and standardization of protocols is carried out by a number of international organizations, which, along with a variety of types of networks, has given rise to a large number of different protocols. The most widely used are the protocols developed for the ARPANET and used in the global Internet, protocols open systems International Organization for Standardization (ISO - International Standard Organization), protocols of the International Telecommunication Union (International Telecommunication Union - ITU, formerly called CCITT) and protocols of the Institute of Electrical and Electronics Engineers (IEEE - Institute of Electrical and Electronics Engineers). Internet protocols are collectively known as TCP/IP. The ISO protocols are seven layers and are known as the Open Systems Interconnection Basic Reference Model (OSIM) protocols).
3.3 Open Systems Interconnection Reference Model (OSI)
Basic EMIS is a model adopted by ISO to describe the general principles of interaction between information systems. EMWOS is recognized by all international organizations as the basis for the standardization of information network protocols.
In EMWOS, an information network is considered as a set of functions that are divided into groups called levels. The division into levels allows you to make changes to the means of implementing one level without restructuring the means of other levels, which greatly simplifies and reduces the cost of upgrading tools as technology develops.
EMOS contains seven levels. Below are their numbers, names and functions.
7th level - application (Application): includes tools for managing application processes; these processes can be combined to perform assigned tasks, exchange data with each other. In other words, at this level, those data that are to be transmitted over the network are determined and formatted into blocks. The level includes, for example, such means for interaction application programs, as receiving and storing packages in "mailboxes" (mail-box).
6th level - representative (Presentation): data presentation functions (coding, formatting, structuring) are implemented. For example, at this level, the data allocated for transmission is converted from the EBCDIC code to ASCII, and so on.
5th level - session (Session): designed to organize and synchronize the dialogue conducted by objects (stations) of the network. At this level, the type of communication (duplex or half-duplex), the beginning and end of tasks, the sequence and mode of exchange of requests and responses of interacting partners are determined.
4th level - transport (Transport): designed to manage end-to-end channels in the data network; this layer provides communication between endpoints (as opposed to the next network layer, which provides data transfer through intermediate network components). The functions of the transport layer include multiplexing and demultiplexing (assembly-disassembly of packets), detection and elimination of errors in data transmission, implementation of the ordered service level (for example, the ordered speed and transmission reliability).
3rd level - network (Network): at this level, packets are formed according to the rules of those intermediate networks through which the original packet passes, and packets are routed, i.e. definition and implementation of routes along which packets are transmitted. In other words, routing is reduced to the formation of logical channels. A logical link is a virtual connection between two or more network layer entities that allows data to be exchanged between these entities. The concept of a logical channel does not necessarily correspond to some physical connection of data transmission lines between the connected points. This concept is introduced to abstract from the physical implementation of the connection. Another important function of the network layer after routing is to control the load on the network in order to prevent congestion that adversely affects the operation of the network.
2nd layer - channel (Link, data link layer): provides data exchange services between logical objects of the previous network layer and performs functions related to the formation and transmission of frames, detection and correction of errors that occur at the next, physical layer. A link layer packet is called a frame because a packet at previous layers may consist of one or more frames.
1st layer - physical (Physical): provides mechanical, electrical, functional and procedural means for establishing, maintaining and disconnecting logical connections between logical objects of the link layer; implements the functions of transferring data bits through physical media. It is at the physical level that the representation of information in the form of electrical or optical signals, the transformation of the waveform, the choice of parameters of the physical media for data transmission are carried out.
In specific cases, there may be a need to implement only a part of these functions, then, accordingly, only a part of the levels are available in the network. So, in simple (non-branched) LANs, there is no need for network and transport layer facilities. At the same time, the complexity of the link layer functions makes it expedient to divide it into two sublevels in the LAN: medium access control (MAC) and logical link control (LLC - Logical Link Control). The LLC sublayer, in contrast to the MAC sublayer, includes a part of the link layer functions that are not related to the characteristics of the transmission medium.
Data transmission over branched networks occurs using encapsulation/decapsulation of data chunks. Thus, a message that has arrived at the transport layer is divided into segments that receive headers and are transmitted to the network layer. A segment is usually referred to as a transport layer packet. The network layer organizes the transfer of data through intermediate networks. To do this, the segment can be divided into parts (packets), if the network does not support the transmission of segments as a whole. The packet is supplied with its own network header (i.e. encapsulation occurs). When transferring between nodes of an intermediate LAN, encapsulation of packets into frames is required with a possible breakdown of the packet. The receiver decapsulates the segments and reconstructs the original message.
Basic elements of a data transmission network (DTN)
Data transmission medium - a set of data transmission lines and interaction blocks (i.e. network equipment, not included in the data stations) intended for data transmission between data stations. Communication media can be shared or dedicated to a specific user.
Data line - the means that are used in information networks to propagate signals in the right direction. Examples of data transmission lines are coaxial cable, twisted pair wires, light guide.
The characteristics of data lines are the dependence of signal attenuation on frequency and distance. Attenuation is usually estimated in decibels, 1 dB = 10 * lg (P1 / P2), where P1 and P2 are the signal power at the input and output of the line, respectively.
For a given length, we can talk about the bandwidth (bandwidth) of the line. Bandwidth is related to the rate at which information is transmitted. There are baud (modulation) and information rates. Baud rate is measured in bauds, i.e. by the number of discrete signal changes per unit of time, and information - by the number of bits of information transmitted per unit of time. It is the baud rate that is determined by the bandwidth of the line.
If N bits are transmitted in the baud interval (between adjacent signal changes), then the number of gradations of the modulated carrier parameter is 2 N . For example, with a number of gradations of 16 and a speed of 1200 baud, one baud corresponds to 4 bits / s and the information rate will be 4800 bits / s.
The maximum possible information rate V is related to the bandwidth F of the communication channel by the Hartley-Shannon formula (it is assumed that one change in the signal value occurs in log 2 k bits, where k is the number of possible discrete signal values)
V = 2*F*log 2k bps,
since V \u003d log 2 k / t, where t is the duration of transients, approximately equal to 3 * T B, and T B \u003d 1 / (2 * p * F), k \u003d 1 + A, where A is the signal / hindrance.
Channel (communication channel) - means of one-way data transmission. An example of a channel would be a frequency band allocated to a single transmitter in radio communications. In some line, you can form several communication channels, each of which transmits its own information. In this case, the line is said to be divided between several channels. There are two methods of dividing the data line: time multiplexing (otherwise time division or TDM), in which a certain time slice is allocated to each channel, and frequency division (FDM - Frequency Division Method), in which a certain frequency band is allocated to the channel.
Data transmission channel - means of two-way data exchange, including data end equipment (node) and data transmission line.
Components of SPD. This is a set of hardware for representing information in an encoded form and converting it in order to effectively distribute signals over the physical communication medium (FSS) (communication channel). In accordance with the above definition, a data transmission channel can be represented as consisting of two main parts: data transmission equipment and a physical communication medium through which information is transmitted. Variants of data transmission channel structures are shown in fig. 4, a-c.
Network data transmission path. This is a set of parallel-connected communication channels organized in lines of various types using frequency or time multiplexing equipment, signal conversion devices, modems and devices for improving the reliability of information transmission.
The functional purpose of each of the specified parts of the channel and data transmission path determines their technical design. Structurally, the data transmission equipment (DTE) is connected to the communication line through special hardware (communication interfaces), which are performed on the basis of standard solutions, requirements and recommendations. The international standards that define the connection of APDs to the physical environment are referred to as the X-series recommendations (MKKTT), in particular X.21 and X.21 bis. In our country, communication interfaces are called JOINTS, denoted by capital letters C with a number on the right: C1, C2, C3, C4. JOINT C1 determines the structure, composition and logic of the interaction of connecting circuits between the ATM and the physical communication medium of the FSS (Fig. 1.20, a). It also sets the transmission parameters (speeds, type of communication line, etc.) C2 JOINT defines the parameters of the data exchange circuits between the data terminal equipment of the DTE and the ATM during serial data input / output by one or another subscriber system (SS). In the subscriber system (AS), the exchange and transmission between individual devices (terminal subscribers) (OA) is carried out in parallel, i.e., signals are transmitted simultaneously over a whole group of trunk lines (circuits), which also have standard interfaces(standard IRPR-interface-radial parallel). When connecting a subscriber system to a data transmission channel, firstly, it is necessary to ensure pairing, which is performed using adapters (A) through the IRPR, and secondly, pairing the adapter with a data transmission channel and, if necessary, in case of transmission to a significant
distance transition from parallel to serial exchange through JOINT C2.
Figure 4 - Data link structure
The operation of the data transmission channel can be organized in various ways: to transmit data in only one direction (simplex DDS) (Fig. 4, c), change the transmission direction (half-duplex DDS) (Fig. 4, b) and, using two lines, introduce simultaneous transmission in two directions (duplex SPT), fig. 4. a.
As can be seen from fig. 4, a-c, the main components of the data transmission channel are: destination-recipient 0.4; with a device for receiving PR information and a sender OL, with a transmitter PC, an encoder K 0 and a decoder DC. In the scheme, the so-called continuous communication channel NKS can be distinguished, which includes communication lines, receiving DM and transmitting M modems.
A continuous channel is characterized by the bandwidth , the noise level Rsh, attenuation and other parameters. When connected to the transmitter of the encoder, decoder and error protection devices, on the basis of a continuous channel, a discrete channel(DKS).
To establish physical and logical links between the source and the information transmission system, it is necessary to organize pairing, which is carried out according to the principle of matching the speed of selecting messages by the source and the speed of their transmission over the communication channel. In this case, the main coordinating principle of the source of messages with the communication channel (this equally applies to the receiver and the subscriber) is the coordination of all elements of the information transmission system according to the codes and coding methods used.
In the general case, coding is understood as the process of presenting messages using special elements in accordance with a set of rules that make it possible to effectively implement the transmission, processing of information and other information processes.
As is known from information theory, for a continuous channel, the most important characteristic is its throughput, which can be calculated as follows:
where is the channel bandwidth;
P s, P w -signal and noise power.
It follows from the formula that there are two ways to increase bandwidth channels: increasing the bandwidth of the communication channel, increasing the signal-to-noise ratio.
IS uses methods that implement each of these paths. In particular, if it is required to provide high message rates, high-frequency coaxial cables or fiber-optic lines are used as a continuous channel, which have a relatively low noise level and allow the transmission of a large number of pulses per unit time.
In a continuous channel, modulation, demodulation, filtering and other signal conversions are also performed for the effective flow / processes of information transmission.
A continuous channel does not allow to meet the increased requirements for information transfer processes imposed on information networks. The solution to the problem is in application discrete transmission information and its noise immunity coding.
By the nature of the physical data transmission medium (PD), data transmission channels are distinguished on optical lines communication, wire (copper) communication lines and wireless. In turn, copper channels can be represented by coaxial cables and twisted pairs, and wireless channels can be represented by radio and infrared channels.
Note
If you still remember what a MIME data type is, then by looking at the names of data encoding methods given above, you will immediately see that these are just MIME types. It is with their help that coding methods are set.
In the vast majority of cases, the application/x-www-form-uriencoded encoding method is used. By the way, it is the one that is used by default if the encoding method is not set. The multipart/form-data encoding method is used if you are going to send files to a Web server; it provides appropriate conversion of binary data. The last method, text/plain -- presents the data as plain text, which can be useful if the form data will be sent via e-mail(sometimes this method of data transfer is also used).
So, we figured out the data encoding. It remains to be seen how this data is transmitted over the Network channels.
As you already know, to send data over the Internet, and indeed over any local or global computer network, a special set of rules is used, called a protocol. The protocol defines how data will be encrypted and packaged for subsequent transmission over the network. Naturally, both the transmitting and receiving programs must support the same protocol in order to "understand" each other. (Otherwise, there will be a so-called incompatibility according to the data transfer protocol, a very unpleasant thing.) Actually, it has already been said about Internet protocols and there is no point in repeating it now.
You also know that Web pages and their associated files (graphics, sounds, archives, etc.) are sent over the Web using HTTP protocol. It is also used for data transmission, and two methods of data transmission are provided for this. Both methods are widely used in Internet programming and have their own advantages and disadvantages. Let's take a look at them.
The first method is called GET by the value of the corresponding form parameter. When used, the data is passed as part of the Internet address in the HTTP request.
As you remember, in order to get the file it needs from the Web server, the Web browser sends a so-called HTTP request to the server, which includes the Internet address of the required file. So, data can be transferred as part of this address.
Take, for example, the following data set just above:
name1 = Ivan surname = Ivanovich name2 = Ivanov age = 30
Now let's prepare it for sending via the GET method (the data itself is in bold):
As you can see, the data sent using the GET method is placed at the very end of the Internet address and separated from it by a question mark. In this case, the pairs "name" = "value" are separated from each other by the sign "commercial and" ("&"). Everything is very simple and clear.
Such simplicity and clarity of data presentation is the main advantage of the GET method. As they say, everything is in sight. It also greatly simplifies debugging Web pages: since the address passed to the Web server is displayed in the address bar of the Web browser, you can always see what was passed. (However, as you understand, confidential data cannot be transmitted by this method - everyone who stands behind you will see it.)
http://www.mysite.ru/bin/choose.exe?chapter=3
As you can see, these are actually links to a server program containing one chapter parameter and its value. This means that all other pages of such a site are dynamically generated by the server program, based on the received parameters. According to this principle, directory sites, program catalog sites, electronic stores and other sites containing a large amount of classified information are often built.
Unfortunately, the GET method has a huge drawback: it cannot transfer large amounts of data. This is due to the limitation imposed by the standards on the length of the Internet address: no more than 256 characters. Subtract from this the length of the actual address of the server program, and you get the maximum allowable size of your data. The second drawback of the GET method is the other side of its virtue. The data it sends is publicly visible and can be easily read in the address bar of a web browser.
The GET method should be used if the data sent to the server program is obviously small and not secret. In particular, it is used to send keywords to search engines, in websites built on the basis of a server program (see above), etc. If you need to send bulky or sensitive data, use the second transmission method, called POST.
The POST method transmits data to the server program in the same HTTP request, but not as part of the Internet address, but in the form of so-called additional data. Since the size of the extra data is not limited (at least it can be very large), you can transfer anything you want, in any quantities. In particular, even files can be transferred to the Web server in this way.
Advantages of the POST method: no restrictions on the amount of transmitted data and their "invisibility". Disadvantages: difficult to decrypt data and difficult to debug. The POST method transmits, for example, personal data, addresses of buyers in electronic stores, literary works on the sites http://www.stihi.ru and http://www.proza.ru, etc. In general, something that has large volumes.
As they say, the WWWC committee intends to abandon the GET method altogether and transfer all data using the POST method. So far, the GET method has simply been declared deprecated for use in newly created sites, but in fact it is still supported by Web browsers.
I talked about digital signals. Why are these digital signals so good? As strange as it may sound, digital signals are analog in nature, as they are transmitted by changing the value of voltage or current, but they transmit signals with previously agreed levels. At their core, they are discrete signals. What does the word "discrete" mean? Discrete - this means consisting of separate parts, separate, intermittent. Digital signals are just discrete signals, since they have only TWO STATES: "active" and "not active" - "there is voltage/current" and "there is no voltage/current".
The main advantage of digital signals is that they are easier to transmit and process. For transmission, voltage is most often used. Therefore, two states are assumed: the voltage is close to zero (less than 10% of the voltage value) and the voltage is close to the supply voltage (more than 65% of the value). For example, at a circuit supply voltage of 5 Volts, we get a signal with a voltage of 0.5 Volts - "zero", but if 4.1 Volts - "one".
Serial method of information transfer
There are just two wires, an electrical signal source and an electrical signal receiver, that are attached to these wires.
This is the PHYSICAL LEVEL.
As we have already said, we can only transmit two signals on these two wires: "there is voltage/current" and "there is no voltage/current". What methods of information transfer can we implement?
The easiest way - there is a signal (the light is on) is ONE, there is no signal (the light is off) is ZERO
If you think about it, you can come up with a few more different combinations. For example, take a wide impulse as one, and a narrow impulse as zero:
Or even take the front and cutoff of the pulse as one and zero. Below is a picture, if you forgot what the front and cutoff of the pulse are.
And here is the practical implementation:
Yes, you can come up with as many different combinations as you like. if the "receiver" and "sender" agree on the reception and transmission. Here I have just given the most popular ways to transmit a digital signal. That is, all these methods are PROTOCOLS. And, as I said, you can invent a lot of them.
Communication speed
Imagine a picture... Students, there is a lecture... The teacher dictates the lecture, and the students write it down
But if the teacher very quickly dictates a lecture and, in addition, this lecture on physics or mathematical analysis, then as a result we get:
Why did this happen?
From point of view digital transmission data, we can say that the speed of data exchange between the "Sender" and the "Receiver" is different. Therefore, there may be a real situation when the “Receiver” (student) is unable to receive data from the “Sender” (teacher) due to a data transfer rate mismatch: the transfer rate may be higher or lower than that to which the receiver (student) is configured .
This problem is solved in different serial data transmission standards in different ways:
- preliminary agreement on the speed of data transfer (negotiate with the teacher to dictate the lecture slower or a little faster);
- before transmitting information, the “Sender” transmits some service information, using which the “Recipient” adjusts to the “Sender” (Teacher: “Whoever does not record this lecture in full will not receive credit”)
Most often, the first method is used: the required data exchange rate is pre-set in communication devices. To do this, a clock generator is used, which generates pulses to synchronize all nodes of the device, as well as to synchronize the communication process between devices.
flow control
It is also possible that the “Recipient” (student) is not ready to receive the data transmitted by the “Sender” (teacher) for any reason: busy, malfunction, etc.
This problem is solved in various ways:
1) At the protocol level. For example, it is stipulated in the exchange protocol: after the “Sender” transmits the service signal “start of data transmission” for a certain time, the “Receiver” is obliged to confirm the acceptance of this signal by transmitting a special service signal “ready to receive”. This method called "software flow control" - "Soft"
2) At the physical level- additional communication channels are used, through which the "Sender" BEFORE transmitting information requests the "Recipient" about its readiness to receive). This method is called "hardware flow control" - "Hard";
Both methods are very common. Sometimes they are used simultaneously: both at the physical level and at the exchange protocol level.
When transmitting information, it is important synchronize the operation of the transmitter and receiver. The method of setting the communication mode between devices is called "synchronization". Only in this case, the "Recipient" can correctly (reliably) receive the message transmitted by the "Sender".
Communication modes
Simplex communication.
In this case, the Receiver can only receive signals from the sender and cannot influence him in any way. It's mostly TV or radio. We can only watch or listen to them.
Half duplex communication.
In this mode, both the sender and the receiver can send signals to each other alternately if the channel is free. Great example half-duplex communication is a walkie-talkie. If both subscribers will crackle each into their walkie-talkie at the same time, then no one will hear anyone.
- First, first. I am second. How is it heard?
- I can hear you normally, hang up!
Only the sender can send a signal, in which case the receiver receives it. Or the receiver can send the signal, in which case the sender receives it. That is, both the sender and the recipient have equal rights to access the channel (communication line). If both of them simultaneously transmit a signal to the line, then, as I said, none of this will work.
duplex communication.
In this mode, both reception and transmission of a signal can be carried out in two directions at once. simultaneously. A vivid example of this is a conversation on a mobile or home phone, or a conversation on Skype.
Information about the surname, name, patronymic, place and date of birth, as well as his address, family, social status, income and assets, education are classified as personal information, which cannot become public without the consent of the person himself. An exhaustive definition of this concept is specified in the law "On Personal Data", adopted back in 2006.
Data transfer is possible:
- (on the territory of a foreign state);
- internal (on the territory of the Russian Federation).
REFERENCE! The collection and storage of this information is carried out by operators (state, municipal institutions or commercial organizations). They are also responsible for maintaining confidentiality.
Data protection is not required only if it is publicly available or anonymized. For example, if information about a person is posted on his website or has already been used in the media or other open sources, or if the information is presented in the form of statistics for scientific purposes.
Can it be transferred to other organizations?
You can transfer personal information about a person, but for this you need to enlist him. For example, the employer must obtain written approval from the employee, except when the transfer of information is necessary in order to prevent a threat to his life and health (Article 88 of the Labor Code of the Russian Federation). It is also not allowed to transfer information for commercial purposes, for example, for the subsequent distribution of spam or advertising.
What employee data is protected by law:
We are talking about information that any employee independently transfers to the accounting department or the personnel department when he is registered for work. The employer does not collect this information. It must not fall into the wrong hands, such as the phone company's customer database or any other commercial company.
The employer also does not have the right to demand a report on the health status of the employee., with the exception of those information that relate to the question of the possibility of fulfilling his duties. Information about a person (a completed questionnaire, personal card, certification results, etc.) can only be transferred to specially authorized persons.
Personal information is also transferred when registering in online stores. To do this, the buyer always checks the online form of the agreement about his consent. Information is also transmitted in other cases: from the placement of a child in school and before obtaining a loan.
Who can receive?
You can transfer data to anyone who requests it as part of the conclusion of the contract(including labor) or other activities.
By law all information about the operations of the bank's client must be stored on electronic media for at least five years. In case of revocation of the bank's license, electronic media must be transferred to the Bank of Russia. Only the data of individuals is protected, since the law does not apply to companies.
Customer data is stored in the Client-Bank system, money transfer, as well as on the company's website and other resources. To protect information in banking and other structures, a variety of technical and organizational measures are used, for example, access control, registration, firewall, anti-virus measures, intrusion detection tools. Operators encrypt their archives, documents, communication channels and use MPLS packet switching.
Features of the dissemination of personal information
The transfer of information can be with the consent of their owner or without consent. For instance, a person who gets a job is obliged to transfer information about himself to the company, and if an investigation has been started against him, then no.
It is safe to transfer information to banks, as well as to any other organizations that work with large quantity customers, comply with all data protection requirements and strive to ensure that valuable information does not leak.
With the permission of the owner
With the consent of the owner, data is transferred at any conclusion of the contract as well as employment. In this case, the employee's written consent is required. If the employee's data can only be obtained from a third party, the employer notifies him of the request no later than 5 working days.
IMPORTANT! When data changes, the employee must notify the employer and, within two weeks, provide copies of documents confirming the changes (for example, a marriage certificate confirming the change of surname).
The written consent of the employee is required:
- upon receipt of information from a third party;
- when processing special categories of data.
Special categories include information about race, nationality, political views, religious and philosophical beliefs, health status, intimate life. The processing of this data requires the mandatory written approval of the employee.
Without his consent
Without consent, information is transferred if it is anonymized(for statistical or other scientific purposes) or is publicly available. The processing of biometric data can be carried out without consent only in connection with the administration of justice, for security purposes, within the framework of operational-search activities, investigations.
The consent of the employee is not required if the processing of data is necessary to protect the life, health or other vital interests of the employee, if obtaining his consent is impossible.
Sending procedure
Transferring data is very easy. If consent is required, it must be given in writing or electronically. However, please note that registering on the website of the online store, you can not transfer the pin codes of the card.
REFERENCE! It is also advisable not to make notes about your income, medical and personal information. In other words, if it's possible to reduce the amount of information you're transmitting, then it's best to do so.
How to transfer data to third parties:
- Decide on the set of information that will be transferred.
- Give consent to the transfer.
- Obtain information about a possible withdrawal of consent (for example, an email address where you can send a statement in case you change your mind).
Once the consent has been transferred, it will be possible to start shopping online or performing work duties, using credit, insurance, and so on.
Preparation of documents
The main document confirming the willingness to transfer personal information about yourself is called a written consent.
This may be a document that indicates the date, personal data and contacts, and also gives permission for their transfer. Either the user accepts it by registering on the site or applying for a product or service. In the latter case it will be enough just to put a mark next to the corresponding phrase.
Includes:
Consent is given for the duration of the contract and within 5 years after its expiration.. Withdrawal of consent may be made in writing not earlier than the date of termination of the contract or the date of fulfillment of obligations in accordance with it.
Consent is given to whole line actions: from collection to destruction and transboundary transfer. Processing is carried out by storage, recording on electronic media and their storage, compiling lists, marking. If you register on the site, the operator must explain how consent can be withdrawn and what needs to be done to do this.
Labor contract
At the conclusion of a written contract with the employer, sometimes simultaneous consent is given to the transfer of data. It is issued in the form of a separate clause of the agreement. By signing the contract, the employee simultaneously gives consent. The clauses of the agreement may indicate which data will be processed.
The consent of the employee is valid from the date of conclusion of the contract until the termination of employment and may be withdrawn. After the conclusion of the contract, information about the employee can, for example, be published on the company's website (for example, information about education, age, etc.).
Channels
You can transfer data from hand to hand when you enter into a written contract, through open communication channels (for example, by phone), as well as by e-mail. The transfer can take place within the country or outside it (). Before giving personal information about yourself over the phone or sending it by e-mail, you should make sure that it is really necessary and safe.
Early recall
At any time, even if the data has already been transferred, you can prohibit their processing and storage by other persons. In case of withdrawal of consent, the operator is obliged by law to stop processing and destroy them within a month.
How to revoke permission to process data:
For example, parents of children often refuse further processing and storage of medical data, who transferred them when registering for kindergartens. To do this, a withdrawal of consent is written in the form of a statement addressed to the management of the institution. Residents of the house who protest against the publication of a list of debtors for utilities can take similar actions.
Making an application
REFERENCE! A sample of this document is easy to find on the Web. It is compiled arbitrarily, but with the obligatory indication of contacts, full name. applicant, date and reason for requesting withdrawal of consent.
The application must indicate:
- term of termination;
- a request for written notification of the results of the consideration of the application.
It is necessary to list and what kind of data you need to stop processing. For example, if an application is made for a bank, then we can talk about the address and registration, contacts of employers, telephone numbers (personal and, for example, guarantors, relatives). A copy of the contract and the applicant's passport may be attached to the application.
Restriction on sending your information
If the data owner does not intend to transfer them to other organizations, for example, when concluding a contract, then he can simply refuse to sign it. It is often simply impossible to sign an agreement by imposing a ban on the transfer of data. Refusal to process data makes it impossible to conclude a contract.
Similar You can not opt out of the transfer of data during employment. However, the owner of the data can always revoke them, if he considers it necessary, by writing a revocation statement.
Litigation in case of unauthorized disclosure
REFERENCE! A claim for civil liability is filed only in the event that the operator leaked data and caused harm to the owner of the information (clause 6.1 of article 29 of the Code of Civil Procedure of the Russian Federation
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Communication line generally consists of a physical medium through which electrical information signals are transmitted, data transmission equipment and intermediate equipment. Synonymous with the term communication line(line) is a term link(channel).
The physical transmission medium can be a cable, that is, a set of wires, insulating and protective sheaths and connectors, as well as the earth's atmosphere or outer space through which electromagnetic waves propagate.
Depending on the data transmission medium, communication lines are divided into the following:
§ wired (air);
§ cable (copper and fiber-optic);
§ terrestrial and satellite communications.
Wired (overhead) communication lines are wires without any insulating or shielding braids, laid between poles and hanging in the air. Such communication lines traditionally carry telephone or telegraph signals, but in the absence of other possibilities, these lines are also used to transmit computer data. The speed qualities and noise immunity of these lines leave much to be desired. Today, wired communication lines are rapidly being replaced by cable ones.
cable lines are quite complex structures. The cable consists of conductors enclosed in several layers of insulation: electrical, electromagnetic, mechanical, and possibly also climatic. In addition, the cable can be equipped with connectors that allow you to quickly connect various equipment to it. V computer networks Three main types of cable are used: twisted-pair copper cables, coaxial cables with a copper core, and fiber optic cables.
A twisted pair of wires is called twisted pair. Twisted pair exists in a shielded version , when a pair of copper wires is wrapped in an insulating screen, and unshielded , when there is no insulating wrap. Twisting wires reduces the influence of external interference on the useful signals transmitted over the cable.
Coaxial cable has an asymmetric design and consists of an inner copper core and a braid separated from the core by a layer of insulation. There are several types of coaxial cable that differ in characteristics and applications - for local networks, for global networks, for cable television, etc.
fiber optic cable consists of thin fibers through which light signals propagate. This is the highest quality type of cable - it provides data transmission at a very high speed (up to 10 Gb / s and higher) and, better than other types of transmission medium, provides data protection from external interference.
Radio channels of terrestrial and satellite communications generated by a transmitter and receiver of radio waves. There are a large number of different types of radio channels, differing both in the frequency range used and in the channel range. The ranges of short, medium and long waves (KB, SV and DV), also called amplitude modulation ranges (Amplitude Modulation, AM) by the type of signal modulation method used in them, provide long-distance communication, but at a low data rate. Higher speed channels are those operating on ultrashort wave bands (VHF), which are characterized by frequency modulation, as well as ultra-high frequency bands (microwave or microwaves).
In the microwave range (above 4 GHz), signals are no longer reflected by the Earth's ionosphere, and stable communication requires a line of sight between the transmitter and receiver. Therefore, such frequencies use either satellite channels or radio relay channels where this condition is met.
Almost all the described types of physical data transmission media are used in computer networks today, but the most promising are fiber-optic media. Today, both backbones of large territorial networks and high-speed communication lines of local networks are being built on them.
popular medium is also twisted pair, which is characterized by an excellent ratio of quality to cost, as well as ease of installation. With the help of twisted pair, end subscribers of networks are usually connected at distances up to 100 meters from the hub. Satellite channels and radio communications are used most often in cases where cable communications cannot be used - for example, when passing a channel through a sparsely populated area or to communicate with a mobile network user.
Even when considering the simplest network of only two machines, one can see many of the problems inherent in any computer network, including problems related to the physical transmission of signals over communication lines , without the solution of which any kind of connection is impossible.
V computer science used to represent data binary code . Inside the computer, data ones and zeros correspond to discrete electrical signals. The representation of data as electrical or optical signals is called coding. . Exists various ways encoding the binary digits 1 and 0, for example, potential a way in which one voltage level corresponds to one, and another voltage level corresponds to zero, or impulse a method when pulses of different or one polarity are used to represent numbers.
Similar approaches can be used to encode data and transfer it between two computers over communication lines. However, these communication lines differ in their electrical characteristics from those that exist inside a computer. The main difference between external communication lines and internal ones is their much longer length , as well as in the fact that they pass outside the shielded housing in spaces often subject to strong electromagnetic interference. All this leads to much greater distortion of rectangular pulses (for example, “filling up” of fronts) than inside a computer. Therefore, for reliable recognition of pulses at the receiving end of the communication line, when transmitting data inside and outside the computer, it is not always possible to use the same speeds and coding methods. For example, the slow rise of the pulse front due to the high capacitive load of the line requires the transmission of pulses at a lower speed (so that the leading and trailing edges of neighboring pulses do not overlap and the pulse has time to grow to the required level).
V computer networks apply both potential and impulse encoding of discrete data , as well as a specific way of representing data that is never used inside a computer - modulation(Fig. 3). When modulating, discrete information is represented by a sinusoidal signal of the frequency that the existing communication line transmits well.
Potential or pulse coding is used on high quality channels, while sinusoidal modulation is preferred when the channel introduces severe distortion into the transmitted signals. Usually modulation is used in global networks when transmitting data over analog telephone circuits, which were designed to transmit voice in analog form and are therefore not well suited for direct transmission of pulses.
Used to convert data from one form to another modems. Term "modem" - short for modulator/demodulator. A binary zero is converted, for example, to a low frequency signal, and a unit is converted to a high frequency signal. In other words, by converting the data, the modem modulates the frequency of the analog signal (Fig. 4).
The number of wires in the communication lines between computers also affects the method of signal transmission.
Data transfer can occur in parallel (Fig. 5) or sequentially (Fig. 6).
To reduce the cost of communication lines in networks, they usually strive to reduce the number of wires and because of this they use not parallel transmission of all the bits of one byte or even several bytes, as is done inside a computer, but serial, bit-by-bit transmission, requiring only one pair of wires.
When connecting computers and devices, three different methods are also used, denoted by three different terms. The connection is: simplex, half duplex and full duplex(Fig. 7 ).
A simplex connection is said to be when data moves in only one direction. A half-duplex connection allows data to travel in both directions but at different times, and finally a full-duplex connection is when data travels in both directions at the same time.
Rice. 7. Examples of data flows.
Another important concept is connection switching.
Any communication networks support some way of switching their subscribers among themselves. These subscribers may be remote computers, local networks, fax machines, or simply interlocutors communicating using telephone sets. It is practically impossible to provide each pair of interacting subscribers with their own non-switched (i.e. permanent connection) physical communication line, which they could exclusively “own” for a long time. Therefore, in any network, some method of subscriber switching is always used, which ensures the availability of available physical channels simultaneously for several communication sessions between network subscribers.
Connection switching allows network hardware to share the same physical link between many devices. The two main ways to switch a connection are - circuit switching and packet switching.
Circuit switching creates a single continuous connection between two network devices. While these devices are communicating, no other device can use this connection to transfer its own information - it is forced to wait until the connection is free.
A simple example of a circuit switch is a switch type A-B, serving to connect two computers to one printer. To allow one of the computers to print, you turn a toggle switch on the switch, establishing a continuous connection between the computer and the printer. A point-to-point connection is formed . As shown in the figure, only one computer can print at the same time.
Rice. 6Switching circuits
Most modern networks, including the Internet, use packet switching. Data transfer programs in such networks divide data into pieces called packets. In a packet-switched network, data can travel in one packet at a time, or in several. The data will arrive at the same destination, even though the paths they took may be completely different.
To compare two kinds of connections in a network, let's assume that we interrupted the link in each of them. For example, by disconnecting the printer from the manager in fig. 6 (by moving the toggle switch to position B), you have deprived him of the ability to print. A circuit-switched connection requires an uninterrupted communication link.
Rice. 7. Packet switching
Conversely, data in a packet-switched network can move in different ways. This is seen in fig. 7. Data does not necessarily follow the same path between office and home computers, breaking one of the channels will not result in a loss of connection - the data will simply go the other way. Packet switched networks have many alternative routes for packets.
Packet switching is a subscriber switching technique that has been specifically designed to carry computer traffic efficiently.
The essence of the problem lies in pulsating nature of traffic , which is generated by typical network applications. For example, when accessing a remote file server, the user first browses the contents of that server's directory, which involves a small amount of data transfer. It then opens the required file in a text editor, and this operation can create quite an intensive exchange of data, especially if the file contains large graphical inclusions. After displaying several pages of the file, the user works with them locally for a while, which does not require any network transfer at all, and then returns modified copies of the pages to the server - and this again generates heavy network data transfer.
The traffic ripple coefficient of an individual network user, equal to the ratio of the average intensity of data exchange to the maximum possible, can be 1:50 or 1:100. If for the described session to organize channel switching between the user's computer and the server, then most of the time the channel will be idle. At the same time, the switching capabilities of the network will be used and will not be available to other network users.
In packet switching, all messages transmitted by the network user are broken up at the source node into relatively small parts, called packets. A message is a logically completed piece of data - a request to transfer a file, a response to this request containing the entire file, etc.
Messages can be of arbitrary length, from a few bytes to many megabytes. In contrast, packets can also typically be of variable length, but within narrow limits, such as 46 to 1500 bytes. Each packet is provided with a header that specifies the address information needed to deliver the packet to the destination host, as well as the packet number that will be used by the destination host to assemble the message.
Packets are transported on the network as independent information blocks. Network switches receive packets from end nodes and, based on address information, transmit them to each other, and ultimately to the destination node.
Packet network switches differ from circuit switches in that they have an internal buffer memory for temporary storage of packets if the output port of the switch is busy transmitting another packet at the time the packet is received. In this case, the packet is for some time in the queue of packets in the buffer memory of the output port, and when it reaches the queue, it is transferred to the next switch. Such a data transfer scheme allows smoothing traffic ripples on backbone links between switches and thus using them in the most efficient way to increase network throughput as a whole.
Indeed, for a pair of subscribers, it would be most effective to provide them with a switched communication channel for their sole use, as is given in circuit-switched networks. With this method, the interaction time of a pair of subscribers would be minimal, since data would be transmitted without delay from one subscriber to another.
A packet-switched network slows down the process of interaction of a particular pair of subscribers. However, the total amount of computer data transmitted by the network per unit of time with the packet switching technique will be higher than with the circuit switching technique.
Usually, if the provided access speed is equal, a packet-switched network turns out to be 2-3 times cheaper than a circuit-switched network, that is, a public telephone network.
Each of these schemes circuit switching (circuit switching) or packet switching (packet switching)) has its advantages and disadvantages, but according to the long-term forecasts of many experts, the future belongs to packet switching technology, as it is more flexible and versatile.
Circuit-switched networks are well suited for constant-rate data switching, when the switching unit is not a single byte or data packet, but a long-term synchronous data stream between two subscribers.
Both packet-switched networks and circuit-switched networks can be divided into two classes on a different basis - networks with dynamic switching and networks with constant switching.
In the first case, the network allows a connection to be established at the initiative of the network user. Switching is performed for the duration of the communication session, and then (again, at the initiative of one of the interacting users), the connection is broken. In general, any network user can connect to any other network user. Typically, the connection period between a pair of users during dynamic switching ranges from several seconds to several hours and ends when certain work is performed - transferring a file, viewing a page of text or image, etc.
In the second case, the network does not provide the user with the ability to perform dynamic switching with another arbitrary network user. Instead, the network allows a pair of users to order a connection on a long period[ time. The connection is established not by the users, but by the personnel maintaining the network. The time for which permanent switching is established is usually measured in several months. The always-switched mode in circuit-switched networks is often referred to as a service. dedicated or leased channels.
Examples of networks that support dynamic switching mode are telephone networks public, local networks, Internet.
Some types of networks support both modes of operation.
Another problem to be solved in signaling is the problem mutual synchronization of the transmitter of one computer with the receiver of another . When organizing the interaction of modules inside the computer, this problem is solved very simply, since in this case all modules are synchronized from a common clock generator. The problem of synchronization when connecting computers can be solved in different ways, both by exchanging special clock pulses over a separate line, and by using periodic synchronization with predetermined codes or pulses of a characteristic shape that differs from the shape of data pulses.
Asynchronous and synchronous transmission. When exchanging data at the physical level, the unit of information is a bit, so the means physical layer always maintain bit synchronization between receiver and transmitter.
However, if the quality of the communication line is poor (usually this applies to telephone switched channels), to reduce the cost of equipment and increase the reliability of data transmission, additional funds byte-level synchronization.
This mode of operation is called asynchronous or start-stop. Another reason for using this mode of operation is the presence of devices that generate data bytes at random times. This is how the keyboard of a display or other terminal device works, from which a person enters data for processing by a computer.
In asynchronous mode, each byte of data is accompanied by special start and stop signals. The purpose of these signals is, firstly, to notify the receiver of the arrival of data and, secondly, to give the receiver enough time to perform some timing-related functions before the next byte arrives.
The described mode is called asynchronous because each byte can be slightly offset in time relative to the bitwise cycles of the previous byte.
The tasks of reliable exchange of binary signals represented by the corresponding electromagnetic signals in computer networks are solved by a certain class of equipment. In local networks, these are network adapters, and in global networks, data transmission equipment, which includes, for example, the considered modems. This equipment encodes and decodes each information bit, synchronizes the transmission of electromagnetic signals over communication lines, checks the correctness of the transmission by the checksum, and can perform some other operations.
3. What communication lines are used in computer networks?
4. What lines of communication are the most promising?
5. How are binary signals transmitted on the network? What is modulation?
6. What is the modem used for?
7. What is serial and parallel data transmission?
8. What is a simplex, half duplex and full duplex connection?
9. What is connection switching?
10. What are the two main ways to switch a connection?
11. What is packet switching and what is its advantage?
12. When is it appropriate to use circuit switching?
13. Explain the concepts of asynchronous and synchronous data transfer?
